The nuclear bromination of polystyrene has been the subject of many patent applications and other publications. Summaries of some of this work can be found, for example, in Houben-Weyl, volume XIV/2, 680 or in H. Vogel, "Flammfestmachen von Kunststoffen" (Flameproofing of Plastics"), A. Huthig Verlag (1966), 66 to 67. A common feature of all of the procedures described in these publications is that some of the aliphatically bonded hydrogen atoms are also replaced by halogen during the bromination. As a result, such products cannot be used for a number of applications, since they split off hydrogen bromide at temperatures of only about 200.degree. to 250.degree. C. Even when they contain only very small amounts of aliphatically bonded bromine, they develop a dark discoloration at temperatures above 200.degree. C.
German Auslegeschrift 2,537,385 (U.S. Pat. No. 4,074,032) describes a process for the bromination of hydrogenated oligomeric styrenes, by which nuclear bromination products are obtained which are heat-stable up to 320.degree. C. Such oligostyrenes have a molecular weight of 400 to 8,000. However, it is desired to have available nuclear-brominated, heat-stable polystyrenes of customarily used higher molecular weights. These are desired, inter alia, since, because of their lower solubility and volatility, improved physiological characteristics can be expected with these polymers. This is important, for example, for the production of plastics with a flameproof finish. Moreover, the fact that the oligomeric styrenes have to be hydrogenated prior to bromination by this process, which is in itself known and is carried out with conventional agents, must also be regarded as a disadvantage. Furthermore, as can be seen from all of the examples of this reference, the stability is partly achieved by adding specific phosphites.
Since it has hitherto not been possible to manufacture nuclear-brominated, heat-stable polystyrenes by bromination, it has been proposed (see German Auslegeschrift No. 1,544,694, column 1, lines 63 to 67), to use poly-(tri-bromostyrene) which has been manufacture by polymerization of tribromostyrene. This manufacturing process is, however, industrially disadvantageous, since both the synthesis of tribromostyrene and the polymerization thereof are expensive processes.